#!/bin/bash

echo hello
echo $?
#$?读取最后执行命令的退出码

abcde # this command not exits
echo $?

true # true 是 shell 内建命令,什么事都不做,就是 shell 返回 0
echo "exit status of true=$?"

! true # blank between ! and true
echo  "exit status of \"! true\"=$?"
